1. Field
The present invention relates to liposomes for delivering an active ingredient to a subject, and methods of delivering the active ingredient to a target site of a subject using the liposomes.
2. Description of the Related Art
Liposomes consist of at least one lipid bilayer membrane enclosing an aqueous internal compartment. Liposomes may be characterized by membrane type and by size. Small unilamellar vesicles (SUVs) may have a single membrane and have a diameter in a range of about 20 nm to about 50 nm. Large unilamellar vesicles (LUVs) may have a diameter of about 50 nm or greater. Oligolamellar large vesicles and multilamellar vesicles may have multiple, usually concentric, membrane layers and have a diameter of about 100 nm or greater. Liposomes with several non-concentric membranes, i.e., several smaller vesicles contained within in a large vesicle, are termed multivesicular vesicles.
Liposomes may be formulated to carry therapeutic agents, drugs or other active ingredients either contained within the aqueous interior space (water-soluble active ingredient) or partitioned into the lipid bilayer (water-insoluble active ingredient). In addition, a hydrophobic active ingredient such as cholesterol may be contained in a micelle. As used herein, “micelle” refers to an aggregate of surfactant molecules comprising a hydrophobic interior. A micelle comprising a hydrophobic active ingredient may be contained within the liposome aqueous interior space.
The delivery of hydrophobic drugs may be performed by emulsion, the use of co-solvents, and by micelles. In the case of the liposomes, hydrophobic drugs may be contained within the lipid bilayer of the liposome, which may affect a property of the lipid bilayer. As a result, the stability or stimulus-sensitivity of the lipid bilayer may not be retained. Additionally, hydrophobic drugs contained within the lipid bilayer of the liposome may not be efficiently released due to strong coherence between the hydrophobic drugs and the lipid bilayer.
There has been research on the use of albumin as a carrier for hydrophobic drugs since albumin has a hydrophobic pocket and accordingly may strongly bind to hydrophobic drugs. However, when albumin is used as a drug carrier, targeting with respect to diseased tissues may not be conducted. Additionally, there may be undesirable side-effects for treatments comprising albumin-bound drugs.
Therefore, a need remains for liposomes that provide the controlled release of active ingredients to act on the target site of a subject.